Explanation of APRS by its Author

AUTOMATIC PACKET REPORTING SYSTEM (APRS)
APRS is a shareware program that takes advantage of the availability
of inexpensive GPS receivers to display the locations of moving stations
on your PC. By connecting your PC computer to any radio network
via an inexpensive ($130) radio data modem, then all stations can see
the movements of all other stations. APRS permits any number of stations to
exchange data just like voice users but without the complexity of
maintaining separate point-to-point links. The primary APRS display
screen is the MAP display. To help mobile units find each other, there
are radio nets standardizing on several radio channels:

APRS recognizes that one of the greatest real-time needs at any
special event or emergency is the tracking of key assets:

Where is the Event Leader?

Where are the emergency vehicles?

What's the Weather at various points in the County?

Where are the power lines down?

Where is the head of the parade?

Where are the VIP's?

Where is the mobile TV camera?

Where is the hurricane?

WHERE IS THE FINISH LINE???

Included on the distribution disk are several README text files on
applications of APRS such as for weather nets, direction finding, plotting
satellite contacts, and tracking mobiles. In addition to the map display
from any range from .5 to 4000 miles, there are several other data screens:

LATEST LIST - A list of the latest STATUS beacon from each station

POSITIONS - A list of all station posits

MESSAGES - Operator-to-operator message to or from your station

BULLETINS - A page for BULLETIN ANNOUNCEMENTS to all stations

TRAFFIC - A list of the last 23 lines of messages from ALL stations

ALL LOG - A time sequenced log of every new beacon or message sent

HEARD LOG - Shows a 24 hour history of who is on the air

DIGIPEATERS - Displays routing information

STATION TRACKING. Although APRS automatically tracks mobile stations
interfaced to GPS or LORAN navigation, it also easily tracks manual
reports. Any station can place an object on his map including himself
and within seconds that object appears on all other station displays.
In the example of a parade, as each checkpoint comes on line, its position
is instantly displayed to all in the net. Whenever a station moves, he
just updates his position on his map and that movement is transmitted to
all other stations. To track other event assets, any operator can simply
maintain the positions and movements of all assets on his screen, all other
displays running APRS software display the same displays. There is also
a Tracking command on the P display that will cause APRS to keep the map
display always centered on a selected object.

SPACE APPLICATIONS: Some HAM radio satellites may not only transmit their
current location, but can also be used for relaying station position
reports between ground stations over large areas. The value of the map
displays are in their ability to help students visualize the three
dimensional geometry of an overhead pass.

FOX HUNTING OR DIRECTION FINDING: APRS is an excellent tool for plotting the
location of a hidden transmitter, balloon, or interfering signal. APRS will
display the intersection of bearing lines from a number of reporting stations
and also overlapping signal strength contours if only signal strengths are
reported. Finally, APRS includes the Fade-Circle Search and Rescue technique
which can be used by a mobile with only an OMNI antenna to locate a hidden
transmitter.

WEATHER STATION REPORTING: APRS position reports can also include the wind
speed and direction, as well as other important weather conditions. APRS
supports a serial interface option to the ULTIMETER-II home weather station.
With this interface, your station includes WX conditions in your position
report for display at all other stations in the network and you appear
as a bright blue circle, with a line indicating wind speed and direction.

FREQUENCY COORDINATION: As more and more digital devices on amateur radio
include APRS position information in their routine BEACONS, APRS makes an
excellent tool for displaying the topology of radio networks as an aid
to frequency coordination.

PROTOCOL - In order to efficiently use the radio channel, APRS assumes that
old information is less important than new information. Therefore, all
packets are redundantly transmitted but at a longer and longer repetition
rate. Each new packet is transmitted immediately, then 10 seconds
later. After every transmission, the period is doubled. After ten
minutes only six packets have been transmitted, and they stabilize to once
every 10 minutes beyond that.

COMMANDS: The keyboard is always active and responds to over a hundred
different commands. Aside from selecting the major displays shown above,
and manipulating the map display, there are several other sub-menu
commands and the message commands:

F1- Help - Select from a MENU of HELP commands

C - Controls - Display a one line status of all control states

F - FILES Menu - For Loading/Saving files, or Replaying tracks

I - Input commands - Used to input posits, DF info or add OBJects to map

O - OPERATIONS - Several commands for normal operations

M - MAP Functions - Functions dealing with maps

W - Weather Menu - Displays the number of beacons per hour per station

R - READ - Displays your incoming and outgoing messages

S - Send - Sends traffic to a station

E - Erase - Erases outgoing traffic lines

K - Kill - Kills incoming traffic lines

T - Traffic - Displays message traffic between other stations

DEMONSTRATION FILE: To see how the APRS system works on our frequency, use
FILES-LOAD to load the file called FREQ579.BK. This file contains all the
local stations on 145.79 MHz in our area. To see the tracking of the GPS
equipped Army/Navy game football run, load the file named FBALL.BK and replay
the file named FBALL.HST and select to see only FBALL, or CHASE1. To see the
Marine Corps marathon event, load MARATHON.BK and replay the MARTHON.HST
file. See Details in README.1st.

REPLAY: The positions of any moving station can be replayed either from
memory or from a file. Tracks are kept in on-line memory until 150 have been
saved, and then are saved to a HISTORY file. During REPLAY, use the Calls
command to toggle on and off the display of call signs, and use the HOME and
page keys to center and zoom the map display if the mobile station moves off
the screen. During replay, use these commands:

FINDING A COPY OF APRS: APRS can be found on this site or on most other
Amateur radio bulletin board systems. All you need is the APRSxx.zip file
and the regional map file for your area, either E, C, W, or SEmapsXX.zip.
You may also find even more local maps for your specific state, such
as GA, CA, OH, TX, MI, IL, IA, and MOmapsxx.zip. After creating an APRS
directory, be sure to use PKUNZIP -d. The -d option assures that the
complete APRS directory structure is re-constructed as you unzip the files.